Electron-beam lithography has developed after the limit was reached in optical lithography as regards the smallest spot that could reasonably be formed by optical means. Electron-beam lithography makes it possible to record significantly smaller pits/grooves on an energy sensitive resist on a wafer for optical or electronic applications.
US2003155532 discloses a device for electron-beam lithography wherein very small pits can be written, using a small beam intensity, by exposing each pit several times during writing thereby avoiding the mutual repulsion between the electrons setting an upper limit for electron density in the beams. A row of electron beams is arranged in the longitudinal direction of the track. Each beam from the row of beams can be controlled, either to be projected onto the track via electron optics, or to be scattered to an electron absorbing position. The control of the row of beams ensures that each time a track position to be exposed passes the projection position of a beam from said row of beams, the beam in question is projected onto the position in question. Furthermore, means are provided for shifting the beams from the row of beams in transverse direction on the track for the purpose of writing a second track simultaneously with the main track. Finally, several rows of beams arranged one beside another for simultaneously writing onto two tracks arranged one beside another are described. By this device one and the same spot on the master disk can be “exposed” to an electron beam from the row of beams a number of times, wherein successive electron beams from said row of beams are used for successive exposures. The controllable means make it possible either to direct a beam from said row of beams through the aperture, similarly to the process of “exposing” the resist on the master disk, or not to direct said beam through the aperture, similarly to the process of “not exposing” the resist on the master disk. In this manner it is ensured that a very short “exposure time” is used for each exposure of the resist to a beam of electrons, whilst a sufficiently long overall “exposure time”, in particular sufficiently long for minimizing the amount of noise in the signal, can be achieved by selecting a sufficiently large number of beams in the row of beams. However, the electron beam lithography method of US2003155532 is used for manufacturing tracks for optical master disks.
WO 2006076740 discloses a related multi-beam synchronous raster scanning lithography system that includes a processor which generates electrical signals representing a desired exposure pattern at an output. A multi-beam source of exposing radiation generates a plurality of exposure beams. A beam modulator receives the electrical signals generated by the processor and modulates the plurality of exposing beams according to the desired exposure pattern. A beam deflector deflects the plurality of exposure beams by a predetermined distance along a first axis, thereby exposing a plurality of pixels along the first axis with the desired exposure pattern. A translation stage moves the substrate a predetermined distance along a second axis to position the substrate for a subsequent exposure of pixels along the first axis that results in a desired overlapping exposure dose profile. In order to accurately control the exposure pattern formed, this lithography system requires that the beam (optical or electron) is energised and de-energised in time, i.e. the beam is turned on and off. This necessitates quite precise knowledge or feedback about the actual position of the beam, which, in turn, sets a limit to the scanning speed of the lithography system. Thus, a faster lithography system is desired.
When producing wafers or substrates with hole or dot arrays today by electron beam lithography, each individual hole and/or dot (element) is addressed separately. Each dot is down to sub-10 nm in diameter, and the registration accuracy of each hole or dot has to be less than 1 nm. This makes it very critical to move the beam accurately and a finite time is spent on each movement making it impossible to decrease the necessary exposure time below a certain limit for any given electron beam lithography system.
Hence, an improved method for performing electron beam lithography (EBL) would be advantageous, and in particular a more efficient and/or reliable method would be advantageous.